Usually in lakes at depths to at least 3.7 m, less commonly in rivers. Haynes (2000) recognizes two subspecies in Michigan, both occurring essentially throughout the State; subsp. guadalupensis with 50–100 teeth per side of the leaf and stems less than 0.8 mm in diameter and subsp. olivacea with 20–40 teeth per side of the leaf and stems more than 1 mm in diameter. However, few of our specimens named subsp. olivacea have stems even to 1 mm in diameter, and no specimens named subsp. guadalupensis have even 50 teeth per side.